340 Good Combo’s where to find here?

340's were THE perfect street performance small block. Run them as is. High compression, 68-71, or low compression, 72 and 73. The only thing I'd change is stainless steel valves, pocket port the heads, and get a custom cam for your intended usage. Get good machining and your in the 13's or better. And you can drive it anywhere, anytime.